Separation and isomerization of alkylsubstituted aromatic compounds using fluoroalkanesulfonic acids

ABSTRACT

1. A PROCESS TO EXTRACT THE MOXT BASIC METHYL-SUBSTITUTED AROMATIC COMPOUND FROM A MIXTURE COMPRISING METHYL-SUBSTITUTED AROMATIC COMPOUND ISOMERS WHICH COMPRISES INTIMATELY CONTACTING SAID MIXTURE AT ABOUT AMBIENT TEMPERATURE WITH AT LEAST ONE FLUOROALKANESULFONIC ACID OF FORMULA RCF2SO3H WHEREIN R=CL, F, CF3, CF2CL, CC2F5, CF3CFCL, C3F7, OR C4F9 AND SUBSEQUENTLY SEPARATING SAID ACID FROM SAID MIXTURE, SAID MIXTURE AFTER   SAID CONTACTING CONTAINING PROPORTIONATELY LESS OF SAID MOST BASIC COMPOUND THAN SAID MIXTURE PRIOR TO SAID CONTACTING.

Nov. 12, 1974 D A.McAuLAY .848.011

SEPARATION AND ISOIERIZATION 0F ALKYL-SUBSTITUTED AROMATIC COMPOUNDS USING FLUOROALKANESULFONIC ACIDS Filed Dic. 29, 1972 3 Sheets-Sheet l FIG. I

l0 mower CARR/5? EXTRACT/0N A ROMA r/c FEED lSOMER/ZA T/ON .FLUOROALKA/VESULFO/V/C AC/D Nov. 12, 1974 J. M CAULAY 3,848,011

SEPARATION AND ISOIERIZATION 0F ALKYL-SUBSTITUTED ARDMATIC COMP UNDS SING FLUOROALKANESULFONTC ACIDS Filed Dec. 29, 1972 3 Sheets-Sheet. 2

FIG. 2

PRODUC T mom r/o FEED FLUOROAL- KANE SUL- FOlV/C ACID PRODUC 7' n BUTA/VE United States Patent Oihce 3,848,011 SEPARATION AND ISOMERIZATION OF ALKYL- SUBSTITUTED AROMATIC COMPOUNDS USING FLUOROALKANESULFONIC ACIDS David A. McCaulay, Homewood, Ill., assignor to Standard Oil Company, Chicago, Ill. Filed Dec. 29, 1972, Ser. No. 319,549 Int. Cl. C07c 5/24, 7/10 US. Cl. 260-668 A Claims ABSTRACT OF THE DISCLOSURE Fluoroalkanesulfonic acids are shown to isomerize methyl-substituted aromatic compounds to mixtures of their isomers without appreciable disproportionation and, in addition, to preferentially extract the more basic isomers from mixtures containing methyl-substituted aromatic compound isomers. Processes for the use of such extraction and/or isomerization in continuous operations ntiliz ing both liquid and gaseous carriers are disclosed herein.

SUMMARY OF THE INVENTION This invention relates to the use of a fluoroalkanesulfonic acid to isomerize and/or extract al'kyl-substituted aromatic compounds and, in particular, to continuous processes for isomerization and/or extraction of methylsubstituted aromatic compounds wherein a mixture of isomers having a given number of carbon atoms can be produced and/or the most basic isomer of said mixture can be selectively extracted at ambient temperature and above, said mixture in general being continuously produced from either a single isomer or a non-equilibrium mixture of isomers by using a fiuoroalkanesulfonic acid as an isomerizing agent to produce a substantially equilibrium mixture.

In accordance with the instant invention an alkyl-substituted aromatic feed, for example, a xylene such as ortho-xylene, ethylbenzene or a mixture of C aromatic isomers, preferably admixed with either a liquid or vapor carrier, is isomerized and/or extracted with, for example, trifluoromethanesulfonic acid to produce one or, optionally, two streams, one essentially meta-xylene and the second essentially orthoand paraxylenes. Separation of the ortho-para mixture may then be accomplished by techniques well known in the art such as fractional crystallization.

BACKGROUND OF THE INVENTION In the past materials such as hydrogen fluoride-boron trifluoride mixtures and fluorosulfonic acid-antimony pentafiuoride mixtures have been used as isomerization catalysts and/or separation substances for aliphatic and aromatic hydrocarbons. These processes have been unsatisfactory to some degree as, for example, the hydrogen fluoride-boron trifluoride system is quite volatile and can only be used in a liquid-liquid extraction scheme. Now it has been found that isomerization and separation of methyl-substituted aromatic hydrocarbons may be accomplished using a fluoroalkanesulfonic acid without utilizing a metal-containing Lewis acid and, more importantly, such an acid may be used in processes wherein separation of catalyst and hydrocarbons is more economical as the hydrocarbons may be released without application of much heat. Thus, back isomerization is substantially reduced. Additionally, the entire operation operates at or near atmospheric pressure so that costly high pressure vessels and auxiliary equipment are not needed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the flow diagram of a technique using a 3,848,011 Patented Nov. 12, 1974 liquid carrier for the continuous production of a mixture of substantially pure orthoand para-xylene from a C aromatic feed composed predominantly of xylenes. FIG. 2 shows the flow diagram of a technique employing a gaseous carrier for the continuous production from a C predominantly-aromatic feed of a stream which is essentially an orthoand para-xylene mixture and a stream which is essentially meta-xylene. FIG. 3 is the flow diagram for a system similar to that shown in FIG. 2 but wherein a gaseous carrier is employed.

STATEMENT OF THE INVENTION FIG. 1 illustrates an embodiment of the instant invention wherein a liquid carrier is used. A C stream containing substantially one or more xylenes (it may also include ethylbenzene and/or associated hydrocarbons) is passed through line 10 into packed extraction tower 11. A low boiling, inert carrier such as n-pentane is introduced into the bottom of packed tower 11 through line 12. A sufiicient amount of n-pentane is added to remove a portion of the xylene from the acid phase. The remainder goes with the acid through heat exchanger 13 into isomerization zone 14. A fluoroalkanesulfonic acid, for example, trifluoromethanesulfonic acid, is brought into the upper part of extraction tower 11 through line 15. The operations in packed tower 11 are carried out at about ambient temperature in such a way as to effect the removal into the acid phase of substantially all of the meta-xylene from the charging stock and reflux. The hydrocarbon passes up through packed tower 11 against a counterflow of acid. The raffinate leaving the top of tower 11 through line 16 consists of the carrier, ortho-xylene and paraxylene plus any other components of the charge stock minus essentially all of the meta-xylene. The various fractions are separated in stripper 17. The bottoms product, consisting of C aromatics is withdrawn through line 18. This product, because it is essentially free of meta-xylene, can be readily separated by a combination of crystalliza tion and fractionation techniques into the individual pure orthoand para-isomers.

Isomerization zone 14 is a small counter-current packed or staged extraction tower and is operated at temperatures between about 70 C. and about 125 C. using contact times that favor substantially complete isomerization to the equilibrium mixture of 20 weight percent ortho-, 20 weight percent paraand 60 weight percent meta-xylene. The acid phase is contacted with a rising stream of recycled carrier coming in via line 19 and essentially all of the hydrocarbon is removed and carried upward through heat exchanger 13 and line 20 into an appropriate section of packed tower 11.

In only a separation of metafrom the ortho-paramixture is what is desired the scheme of FIG. 1 can be altered such that the isomerization reactor is removed and metaxylene removed from the bottom of tower 11.

FIG. 2 illustrates an embodiment of the instant invention where a gaseous carrier is used. A light, inert, condensible gas such as n-butane is passed through line 21 into feed vaporizer 22 where it picks up vapors of the xylene feed kept at temperatures between about 20 C. and about C. The gaseous mixture of n-butane and xylene then passes through line 23 into extraction column 24, which is operated at about the same temperature as vessel 22. The n-butane-xylene gas mixture then passes up the column counter-current to a descending liquid stream of acid, for example, trifluoromethanesulfonic acid. Isomer fractionation occurs as the gas proceeds up the column and the vapors leaving the top through line 25 are essentially free of meta-xylene. The overhead stream is liquefied by the refrigerant in condenser 26 and is passed into stripper 27. In stripper 27 the n-butane is separated from the ortho-para mixture and recycled via line 28 back cumene, mesitylene and mixtures thereof) and tetramethto extraction column 13 via line 21 and column 24 via line ylbenzenes (durene, isodurene and prehnitene and mix- 29. Product is removed through line 42. tures thereof).

Gaseous n-butane enters near the end of column 24 While the invention is described in connection with via line 29 and in the bottom portion of the column strips the specific examples below, it is to be understood that the xylene from the acid phase. The acid is then recycled these are for illustrative purposes only. Many alternatives, via line 30 to the other end of the column. Gaseous prodmodifications and variations will be apparent to those not, rich in meta-xylene, is taken after acid removal in skilled in the art in the light of the below examples and vessel 34, through line 31, condensed in condenser 36, such alternatives, modifications and variations will fall and then passed into stripper 32. The n-butane is taken within the scope and spirit of the appended claims.

otf overhead and recycled via line 33 to column 24. A stream of essentially meta-xylene is removed from the GENERAL EXPERIMENTAL PROCEDURE bottom of stripper 32 through line 37. Each stripping The extraction experiments were carried out in a small column is preferably equipped overhead to remove englass Reactivial. Hydrocarbon and acid were shaken trained product; components 38 and 39, and 40 and 41. for five minutes and allowed to settle for another five A combination extractive distillation-isomerization minutes. The two phases were separated by means of a process using a gaseous carrier is shown in FIG. 3. Operahypodermic syringe. The rafiinate was washed with water. tion is similar to that previously described in FIG. 1 for The acid phase was poured over an equal weight of ice the extraction of isomerization steps. Carrier is introduced and the liberated hydrocarbon portion was collected. into the bottom of extraction column 43 through line 44 The room temperature conversion runs were made in a in amounts sufficient to remove a portion of the meta- 100 milliliter Teflon bottle stirred by a Teflon-encapsuxylene in the descending acid phase. The remainder goes lated magnetic stirring bar. Samples were taken at inwith the acid into heat exchanger 45 and into isomerizatervals. The conversion run at 100 C. was carried out in tion zone 46. This zone is a packed or staged column a 300 milliliter Hastelloy C autoclave. Samples were withand is operated at temperatures between about 70 C. drawn at intervals, cooled, phases separated, and washed and about 125 C. using contact times that favor subwith water. stantially complete isomerization to the equilibrium mix- All products were analyzed by gas chromatography ture of 20 weight percent ortho-, 20 weight percent parausing conventional techniques.

EXAMPLE I.EXTRACTION 013 Cs AROMATICS WITH TRIFLUOROMETHANESULFONIC ACID [2 volumes of hydrocarbon per volume of trifiuoromethanesultonic acid] Run No. 1 Run No. 2 Run No. 3 Run No. 4 Run No. 5

Temp, 25 0. Temp., 25 0. Temp, 25 0. Temp. 0 0. Temp., 25 0.

Feed Rafi Ext Feed Rafi Ext Feed Rafi Ext Feed Ralf Ext Feed Rafi Ext Composition (weight percent) n-Hexane 66. 5 30. 0 66. 1 68. 5 30. 4 0. 0 0. i] 0. U 0. 0 0. 0 O. 0 63. 4 63. 9 49. 1 Benzene 0. O 0. 0 O. 0 0. 0 0. 0 0. 0 0. 0 0. O 0. O 0. 0 0. (3 O. O 0. l 1. 0 Ethylben ne 0. U 0. 0 0. 0 0. 0 0. 0 0. 0 0. 0 Q. 0 O. 0 0. O 0. 0 1S. 3 18. 0 20. 3 para-Xylene O. 0 0. 0 16. 4 16. 6 24. 0 48. 5 51. 1 42. 7 48. 5 51. 4 39. 7 13. 3 17. 8 27. 6 meta-Xylene 15. 4 44. 3 17. 4 14. 8 45. 6 51. 4 48. 6 57. 0 51. 4 48. 6 60. 3 O. 0 0. O 0. 0 0rth -Xy1mm 17 1 25. 7 O. 1 O. 1 0. U 0. 0 U. 0 0. U 0. 1 0. 1 0. 0 0. O 0. 0 0. 0 Diethylbenzene 0. 0 0. 0 0. o o. 0 0. 0 0 0. O 0. 0 0. 0 0. 0 0. O 0. 0 0. 2 2. O Isomer ratios:

meta-ip-Qrtho 1. 006 0. 958 1. 726

meta-to-para l. 06 0- 892 l- 901 1. 06 0. 952 1. 336 1. O5 0. 947 1. 516 para-to-Ethylb 0.996 0. 991 1.358 Beta (single-stage separation factor). 1. 80 2. 13 1. 1. 60 1. 37 Volume of aromatic extracted per 100 volumes of trifluoromethanesulfom'c acid 3 3 35 24 4 META. ext/PARA ext Beta=--- META raft/PARA rafi and 60 weight percent meta-xylene. The acid phase '18 EXAMPLE H EXTRACTION 0F XYLENES WITH contacted with a llSll'lg stream of n-butane gas coming in PERFLUOROBUTANESULFONIC ACID via, line 47 and essentially allhof ti: IlillydlOCaI'IIJDtDIt IS 165-- [2 volumes of hydrocarbon per volume of perfluorobutanesulfonic acid] moved and carried upward t roug eat exc anger 4 R No. 1 R and line 48 mto an appropriate section of tower 43. Acid N0 2 is recycled to tower 43 through line 50 and carrier is -3 P-. recycled to vessel 58, tower 43 and isomerization zone 46 p Rag Ext Feed R fl Ext through lines 56 and S9, :56 and 44, and l nes '56 and 47. composmon (weight The stripping column 53 is preferably equipped overhead percent): with condenser and collector, 54 and 55, to remove enif iggg 3- 4533 trained product. par'ergicylianeu 1%. it 3%:2? i)6:i 56: &;: me a- 31 ene 9. 49.1 55. 1 Fluorijalkaziesulfomc aclds whlch may be m {he Isomer ratios: meta-to-para 0.882 1.39 0.963 1.228 instant inventlon are (a) perfluoroalkanesulfomc acids Beta(sing1e-stage containing one to about five carbon atoms, more preferably, one to about three carbon atoms and, most preferably, one to about two carbon atoms and (b) partially fluorinated alkanesulfonic acids containing a perfluoromethylene group alpha to the functional group and with EXAMPLE IIL-CONVE RSION OF E'IHYLBENZENE [8.75 volumes 0! ethylbenzene per yfilume 0t trltluoromethaucsultonic S lenumber 1 the remaining carbon atoms substituted by a mixture of amp 2 3 4 5 Reaction time (hours)--- 1.0 17. 5 25. 8 90. 0 118. 5

fluorine atoms and another highly electronegative sub Composition (weight pme stlttltmg atom such as 0111011116 and, more preferably, gggztige 2. 1.; 11.2 13.4 y enzene- 5 .4 51.8 CF ClCF SO H or CF CFCICF CO H and, most prefer Lwiethylbeuzenm 0'5 8.2 m2 1 1M bl CF C1CF SO H, 1,4-diethylbenzene 0.7 5.7 6.2 8.0 7.9 f 1 b t d 1 1,Z-diethylhonvnne 0.1 0.1 E P o a y Stltu e aromatics so p e 1,3,5-triethylbenzene 0.3 0.4 1.8 2,1 and/or isomerable by the processes of the instant mveugg g g 3-; 3-?

tion are, trimethylbenzenes (hemimellitene, pseudo- EXAMPLE IV.CONVERSION OF XYLENES Run number 1 2 Feed, milliliters:

para-Xylene 35 meta-Xylene Trifluoromethanesulfome acid Temperature, C

Reaction time, hours Composition (weight percent):

Benzene meta-Xylene 8 What is claimed is:

1. -A process to extract the most basic methyl-substituted aromatic compound from a mixture comprising methyl-substituted aromatic compound isomers which comprises intimately contacting said mixture at about ambient temperature with at least one fluoroalkanesultonic acid of formula ROF SO H wherein R=Cl, F, CF' CF CI, C F CF CFCl, C F or C F and subsequently separating said acid from said mixture, said mixture after said contacting containing proportionately less of said most basic compound than said mixture prior to said contacting.

2. The process of Claim 1 wherein said fluoroalkanesulfonic acid is trifluoromethanesulfonic acid or perfiuoroethanesulfonic acid.

3. The process of Claim 2 wherein said methyl-substituted aromatic compound isomers are xylenes.

4. A process to isomerize a material comprising a methyl-substituted aromatic compound or a non-equilibrium isomeric mixture thereof which comprises:

(a) intimately contacting said material comprising a methyl-substituted aromatic compound or a nonequilibrium isomeric mixture thereof at a temperature between about 70 C. and about 125 C. with a catalyst consisting essentially of at least one fluoroalkanesulfonic acid of formula ROF SO H wherein R=Cl, F, CF CF CI, C 1 CF CFCl, C 1 or C4Fg, and

'(b) subsequently separating said acid from the product of step (a).

5. The process of Claim 4 wherein said fiuoroalkanesulfonic acid is trifiuoromethanesulfonic acid or perfluoroethanesulfonic acid.

6. The process of Claim 5 wherein said methyl-substituted aromatic compound or a non-equilibrium isomeric mixture thereof is a xylene or a mixture of xylenes.

7. A process to isomerize a material comprising a methyl-substituted aromatic compound or an isomeric mixture thereof and to extract from the isomerized product the most basic isomer in said isomerized product which comprises:

(a) intimately contacting said material comprising said methyl-substituted aromatic compound or an isomeric mixture thereof between about 70 C. and about 125 C. with at least one fluoroalkanesulfonic acid of formula ROF SO H wherein R=Cl, F, CF CF Cl, C F CF CFCl, CgF or C F and (b) subsequently separating said acid from the product of step (a) to form a product substantially acid-free, and

(c) intimately contacting said product substantially acid-free at about ambient temperature with at least one fiu-oroalkanesulfonic acid of formula ROF SO H wherein R=Cl, F, CF CF CI, C F CF CFCl, C3137 Or C4F9, and

'(d) substantially removing the acid from the product of step (c).

8. The process of Claim 7 wherein said fluoroalkanesulfonic acid is trifluoromethanesulfonic acid or perfiuoroethanesulfonic acid.

9. The process of Claim 8 wherein said methyl-substituted aromatic compound or an isomeric mixture thereof is a xylene or a mixture of xylenes.

10. A continuous process to isomerize a material comprising a methyl-substituted aromatic compound or an isomeric mixture thereof and to extract from the isomerized product the most basic isomer in said isomerized product which comprises:

(a) intimately contacting said material at a temperature between about C. and about C., at least partially solubilized in an inert carrier, in an isomerization zone with at least one fluoroalk-anesulfonic acid of formula RCF SO H wherein R=Cl, F, 0P CFZCI, C2F5, Cg'Fq, or C4F9 until an essentially equilibrium isomeric mixture is obtained, and

=(b) cooling the product of step (a) to about ambient temperature, and

'(c) intimately contacting in a counter-current extraction zone the product of step (b) with additional said acid to form two streams, a first stream comprising essentially all of the least basic isomers of said essentially equilibrium isomeric mixture and a second stream comprising essentially all of the most basic of said equilibrium isomeric mixture, and

(d) introducing said first stream containing essentially all the less basic isomers into a separation zone wherein the carrier contained in said first stream is separated from said less basic isomers, and

(e) recycling the carrier contained in said first stream,

and

(f) separating the acid from said second stream to give a third stream and an acid stream, and

(g) recycling said acid stream to said counter-current extraction zone, and

(h) introducing said third stream into a separation zone wherein the carrier contained in said third stream is separated from said most basic isomer, and

(i) recycling the carrier contained in said third stream.

References Cited UNITED STATES PATENTS 3,766,286 10/1973 Olah 260668A CURTIS R. DAVIS, Primary Examiner US. Cl. XJR. 260-674 A, 674 SE 

1. A PROCESS TO EXTRACT THE MOXT BASIC METHYL-SUBSTITUTED AROMATIC COMPOUND FROM A MIXTURE COMPRISING METHYL-SUBSTITUTED AROMATIC COMPOUND ISOMERS WHICH COMPRISES INTIMATELY CONTACTING SAID MIXTURE AT ABOUT AMBIENT TEMPERATURE WITH AT LEAST ONE FLUOROALKANESULFONIC ACID OF FORMULA RCF2SO3H WHEREIN R=CL, F, CF3, CF2CL, CC2F5, CF3CFCL, C3F7, OR C4F9 AND SUBSEQUENTLY SEPARATING SAID ACID FROM SAID MIXTURE, SAID MIXTURE AFTER 